1. Field of the Invention
The present invention relates to a magnetic resistance effect element for the purpose of reading an information signal that is recorded on a magnetic medium, and to a manufacturing method therefor.
2. Description of Related Art
In the past, there have been magnetic reading transducers known variously as magnetic resistance sensors (MR sensors) or magnetic resistance heads, and it has been known that these devices are capable of reading data from a magnetic surface with high linear density. The magnetic resistance sensor detects a magnetic field signal via the strength of the magnetic flux detected by the reading element (magnetic resistance effect element) and the resistance thereof, which changes as a function of direction.
Such sensors as this in the past have operated based on the anisotropic magnetic resistance (AMR) effect, whereby the one component of the resistance of the reading element varies in proportion to the square of cosine of the angle formed between the magnetization direction and the direction of the detected current flowing in the element. A detailed description of the AMR effect can be found, for example, in Thompson, "Memory, Storage, and Related Applications" in IEEE Transactions on Magnetics, MAG-11, p. 1039 (1975).
In recent literature, there has been described a more prominent magnetic resistance effect, in which a change in the resistance in a laminated magnetic sensor is attributed to spin-dependent conduction of conduction electrons between magnetic layers separated by a non-magnetic layer, and to spin-dependent conduction dispersion at the accompanying layer boundary.
This magnetic resistance effect is variously known as the giant magnetoresistive effect or the spin-valve effect. This type of magnetoresistive sensor is fabricated from an appropriate material, and provides an improvement in sensitivity over sensors which use the AMR effect, yielding a larger change in resistance. Using this type of sensor, the intraplanar resistance of a pair of ferromagnetic layers separated by a non-magnetic layer is varies in proportion to the cosine of the angle between the magnetization directions of the two layers.
Japanese Unexamined Patent Publication (KOKAI) No. 2-61572 discloses a laminated magnetic structure which yields a large magnetic resistance change that occurs by virtue of anti-parallel alignment of magnetization within a magnetic layer, ferromagnetic transition metals and alloys are given in the above-noted Japanese Unexamined Patent Publication as materials for use in the laminated magnetic structure. It also discloses a structure in which an anti-ferromagnetic layer is added to one of at least two ferromagnetic layers separated by an intermediate layer, and having FeMn as the material of the anti-ferromagnetic layer.
In Japanese Unexamined Patent Publication (KOKAI) No. 4-358310, there is disclosed a magnetoresistive sensor which has two ferromagnetic thin-film layers which are separated by a non-magnetic metal layer, wherein when an applied magnetic field is zero the magnetization directions of the two ferromagnetic thin-film layers intersect orthogonally, the resistance between two non-bonded ferromagnetic layers varying in proportion to the cosine of the angle between the magnetization directions of the two layers, this being independent of the direction of current flowing in the sensor.
In Japanese Unexamined Patent Application publication there is disclosed a magnetoresistive sensor based on the above-noted effect, this sensor including two ferromagnetic thin-film layers which are separated by a thin-film made of a non-magnetic material, wherein when an externally applied magnetic field is zero, the magnetization of an adjacent anti-ferromagnetic layer is maintained perpendicular with respect to the that of the ferromagnetic layer.
In the prior art, because FeMn, which oxidizes easily in air, is generally given as a candidate for use at the anti-ferromagnetic layer making up a spin-valve structure, practical use makes it essential either to add an additive material or to use a protective film. Additionally, in processing after this measure is taken, the characteristics deteriorate, so that the reliability of the finished element cannot be said to be sufficient.
If an NiO film or a CoPt film having good corrosion resistance, is used a method of increasing the ferromagnetic layer reverse magnetic field, a problem arises because of the tendency for hysteresis to occur in the R-H curve.
In view of the above-described drawbacks in the prior art, an object of the present invention is to provide a magnetoresistive effect element which has a large exchange coupled magnetic field applied from the anti-ferromagnetic layer to a fixed layer, and which, because the coercivity of the fixed layer is small, provides good playback characteristics because the amount of hysteresis in the R-H loop is small, and further to provide a method of manufacturing the above-noted element.